1. Field of the Invention
The invention relates to the control of machine tools by adjusting the CNC controllers and the PLC controller in the tool magazine and the machine tool by means of a separate controller.
2. Description of the Prior Art
The operation of machining complex workpieces requires a large number of different machining tools since each tool undertakes special subtasks for completing the workpiece. For this purpose, machining centers have an integrated tool magazine.
Under electronic control, a specific tool is selected for the respective machining step and the spindle of the machine tool is changed. The next machining step can now be carried out using this tool. This operation is repeated until the workpiece is completed.
During each tool change, the machining operation is interrupted until the change has been completely concluded. The change time varies very greatly depending on the type of magazine (chain, matrix), the access methods used (organized or chaotic method) and the number of tool places. A realistic value for a tool change including the provision time is between 30 and 120 seconds for each tool change.
These waiting times for the next tool are generally shortened by coding commands, which instruct a magazine transporting unit to already provide the follow-on tool, inside a computerized numerical controller (CNC controller). With the next change command, only the tool between the spindle and the transporting unit is thus changed. This is considerably faster since the transporting times are dispensed with.
However, the advantage of this optimization fails entirely in the case of short tool paths and short tool machining sequences, that is to say if the machining times of the tool are shorter than the provision times of the magazine used.
In order to minimize these waiting times, it is advantageous to temporarily store (intermediate storage station) and/or provide any desired number of follow-on tools as close to the spindle as possible during long tool machining times.
This manner of loading and unloading tools in machine tools is described, for example, in WO 2006/050551 A2. According to this method, the tools from a magazine are first of all taken over into an intermediate storage station, the tools being simultaneously removed from the intermediate storage station and the machine tool or inserted therein using a changing apparatus during transfer to the machine tool. This method has the disadvantage of delays arising as a result of uncoordinated processes and thus a rise in the cost of the operation of machining the tool.
EP 0 645 721 A1 relates to the control and organization of different multimedia presentations in which overlapping of the presentations is avoided.
The individual presentations are stored in individual memories and are combined in a playback device. The memory playback device is controlled by a central computer (FIG. 1).
DE 601 04 476 T2 describes a tool changing device in which a changing arm can be rotated by the engagement of a cam and a cam follower. As illustrated in FIG. 5 of this reference, the numerical controller has a computerized numerical controller (CNC), a programmable logic controller (PLC) and an input/output interface.
EP 0 553 621 A1 describes a programmable computer controller for machine tools. In a first adaptive control module between the CNC controller and the workpiece to be machined and an adaptive controller for controlling the machine function, control commands are transmitted from the CNC part to the first adaptive control module via an interface between the CNC part and the first adaptive control module, the control commands from the CNC part being able to be influenced using a data input device.
DE 698 28 947 T2 describes a flexible production system with the completion of a machine tool. Individual workpiece transfer units for machining on the spindle heads of the machine tool are indexed using a control unit 50.